It's meant to raise up to $300 million a year to help us capture billions of gallons of water that's usually wasted after a heavy rain storm - and instead clean it and store it for future use. The typical homeowner (figure about a 6,000-square-foot lot) would pay about $83 a year.

DOES L.A. REALLY HAVE A STORMWATER PROBLEM?

Yup. It's a problem that comes from our geography. The L.A. Basin is surrounded by mountains that slope down to the ocean. We don't get a lot of rain, but when we do, it pours out of the mountains in canyons and creeks and rushes toward the ocean.

After some deaths and destruction from floods a century ago, county residents got together and formed the Flood Control District to build dams and channelize our rivers to direct all that fresh clean rainwater water to the ocean. (That's why stretches of the L.A. River are a concrete trench.)

The system eased flooding and destruction, and made it possible to build millions of homes on flood-prone land. But that system wastes billions of gallons of fresh rain water that we could actually use. It captures some of the runoff, directs it to broad empty fields where it filters underground. County engineers say they can more than double the amount of water captured, cleaned and stored if they have more money to build large and small projects in different places.

Concrete stormwater storage caverns being set into place in Sun Valley Park several years ago. They have since been covered over with about five feet of fill dirt. Baseball and soccer fields are placed atop the caverns. (Photo courtesy of Los Angeles County Flood Control District)

GOT ANY EXAMPLES?

Sun Valley Park

One example is a sports field at Sun Valley park. The surrounding area used to flood during heavy rains. So the county dug out the ball field and built in a vast series of underground chambers — like catacombs - to drain the excess runoff from the streets and infiltrate it into the ground.

Marina Del Rey's Oxford Basin

Another project is the Oxford Basin near Marina del Rey. It uses gates to suck in sea water from the nearby Marina, and the water circulates and mixes with surface runoff and stormwater to clean and filter the water. Then gates return the water back to the Marina. It's a way to keep the the water flowing into the marina and the ocean cleaner.

Dirty Urban Drool

Some projects can be as small as converting median strips in the middle of our streets to catch storm runoff and just the dirty urban drool from daily runoff from sprinklers that gets mixed with dirt and grit from our cars. County engineers also have their eyes on parking lots, parks, and other open spaces that instead of shedding water, could be collecting it.

WHY ARE MEASURE W'S BACKERS SUPPORTING IT?

Los Angeles County captures only about one-fifth of the stormwater that flows down from the mountains, and about one-third of the water used in the county comes from groundwater. The rest is imported from other sources. Capturing more stormwater and cleaning it so it can be used would help reduce the amount of imported water needed in the region.

Climate change is making the dry times drier, with fewer light rains and concentrating rainfall into heavier storms with big quantities that come very quickly. So having more ways to capture more rain and store it underground in water aquifers would help the region deal better with droughts.

Capturing rainfall close to where it lands can also reduce the amount of pollution in local waterways and the ocean.

HOW MUCH WILL MEASURE W COST?

Measure W is supposed to create a pot of money - about $300 million dollars a year. If it gets approved by a two-thirds majority, people who own homes and businesses would be charged a new tax on their land. The parcel tax would be 2.5 cents on every square foot of your property that water cannot soak into.

The county Public Works Department figures the typical home on a 6,000-square-foot parcel would pay about $83 dollars a year, with the tax applied only to the impermeable area. You can figure your own tax using the county's Measure W parcel tax calculator at safecleanwaterla.org.

HOW DOES THE COUNTY KNOW HOW MUCH IMPERMEABLE SURFACE A PARCEL HAS?

The county has already done an aerial survey using equipment known as Lidar, which estimates the square footage of roof, driveway, patio and other paved surfaces that create water runoff.

The engineered Dominguez Gap Wetlands in Long Beach filters stormwater and runoff from the Los Angeles River, then the water is siphoned under the river to a spreading ground to the west. (Sharon McNary/KPCC)

IS L.A. COUNTY ENDORSING MEASURE W?

County employees are barred from using their paid time or public money for electioneering or endorsing measures, even ones their elected bosses put on the ballot. In the case of Measure W, they walk right up to the line, talking up the benefits, but refraining from recommending a yes vote.

"It's education, not advocacy," said Kerjon Lee, a spokesman for L.A. County Public Works.

Los Angeles County budgeted nearly $8 million to craft the measure and get it to the ballot. That includes $3.35 million for advertising and community outreach, according to county budget data provided by the Public Works Department.

You might have seen the county's Measure W logo, an upside-down umbrella catching drops of water that come from the handle, which is shaped like a water spout. They also came up with the "Safe, Clean Water" slogan you hear on a lot of radio stations around L.A.

Four of the five elected L.A. County Supervisors voted in favor of placing Measure W on the ballot.

Environmental groups favor it, so do some labor unions because $300 million dollars a year in new revenue can fund a lot of construction and other well-paying jobs.

WHO OPPOSES MEASURE W AND WHY?

Supervisor Kathryn Barger, who represents parts of the San Fernando and San Gabriel valleys voted against putting the measure on the ballot because it was not more narrowly focused on removing pollution from water.

L.A. County Business Federation, which represents thousands of businesses in the area, ended up opposing Measure W because it didn't include a provision to phase it out.

Some of the objections focus on the impact of the new tax on businesses, which tend to have large buildings and parking lots - all taxable areas.

There's also a sense that we're already paying over and over again for clean water in the form of the many state water bonds and other local water fees that show up on our monthly bills.

Get ready for the Nov. 6 election. Here at LAist, we want to make sure Angelenos have all the information they need to cast their votes. To get prepped on deadlines, candidates and ballot measures, check out our Voter Game Plan. And if you liked this election guide, consider supporting us! You can donate here.